Nuclear reactors harness energy from nuclear fission, where atomic nuclei are split, to generate electricity. This controlled chain reaction primarily uses uranium-235 as fuel. While conventional reactors consume fissile fuel, a specialized breeder reactor operates with a distinct objective.
Understanding Breeder Reactors
A breeder reactor generates more fissile material than it consumes, unlike traditional nuclear power plants that deplete their fuel. Its purpose is to extend the nuclear fuel supply by converting abundant, non-fissile materials into usable fuel.
Conventional reactors rely on uranium-235, which constitutes less than one percent of natural uranium. Breeder reactors, however, can utilize uranium-238 (over 99 percent of natural uranium) or thorium-232. These are “fertile” materials, transformable into fissile isotopes within the reactor, allowing use of a much larger fraction of available resources.
Fast breeder reactors (FBRs) are a significant category. They use “fast” or unmoderated neutrons for the breeding process, unlike thermal reactors that use slower, moderated neutrons. FBR designs, often employing liquid metal coolants like sodium, maintain high neutron energies for efficient conversion.
The Process of Fuel Creation
Breeder reactors create new fissile fuel through nuclear reactions involving neutron capture and radioactive decay. This process begins with fertile isotopes like uranium-238 or thorium-232, placed within the reactor core. Neutrons from primary fuel fission are absorbed by these fertile nuclei, transforming them.
For example, a uranium-238 nucleus captures a neutron to become uranium-239. This unstable isotope rapidly decays into plutonium-239. Plutonium-239 is a fissile isotope, capable of sustaining a nuclear chain reaction and becoming new nuclear fuel. Similarly, thorium-232 captures a neutron and decays to form uranium-233, another fissile material.
Fuel creation effectiveness is quantified by the “breeding ratio,” the ratio of new fissile atoms produced to those consumed. For a reactor to be classified as a breeder, this ratio must be greater than one. Breeder reactor design optimizes neutron economy, maximizing neutrons for conversion reactions.
Resource Management and Waste Considerations
Breeder reactors impact nuclear fuel resource management by expanding the usable fuel supply. Conventional reactors utilize less than one percent of mined uranium’s energy, relying on scarce uranium-235. Breeder reactors can extract up to 70-75% of natural uranium’s energy by converting abundant uranium-238 into fissile plutonium-239. Existing stockpiles of depleted uranium, an enrichment byproduct, become a valuable fuel source.
Beyond extending fuel availability, breeder reactors offer advantages in managing radioactive waste. Spent fuel from conventional reactors contains long-lived transuranic actinides, contributing to nuclear waste’s long-term radiotoxicity. Breeder reactors can “burn” or transmute these actinides through fission, reducing waste volume and long-term radioactivity. This process shortens waste decay time to safe levels, from hundreds of thousands of years to centuries.
Global Development and Operational Status
Several countries have pursued breeder reactor technology for energy independence and efficient resource use. The United States developed the Experimental Breeder Reactor I (EBR-I) in 1951, the first reactor to generate electricity from nuclear fission. France, Great Britain, Japan, and the Soviet Union also constructed experimental breeder reactors.
In the early 21st century, Russia, China, and India continue to operate or develop breeder reactor programs. Russia operates the BN-600 and BN-800 fast breeder reactors, contributing to its electricity grid. India’s three-stage nuclear power program relies on fast breeder reactors to utilize its thorium reserves and limited uranium efficiently, with the Prototype Fast Breeder Reactor (PFBR) a key project. Japan also had involvement with its “Joyo” experimental reactor and the “Monju” prototype, though the latter faced operational challenges. These nations pursue the technology to maximize energy potential from nuclear resources and address long-term energy security.